WASHINGTON (AP), Jun 13 - A battle is brewing over President Barack Obama's pick to be the next U.S. ambassador to Iraq, with Senate Republicans calling for the nomination to be withdrawn and the White House and former envoys to Iraq staunchly defending it.

Six Republican members of the Senate Foreign Relations Committee sent a letter to President Barack Obama on Wednesday calling on him to withdraw Brett McGurk's nomination. They cited concerns about his abilities and judgment amid allegations that he acted inappropriately while working at the U.S. Embassy in Baghdad during President George W. Bush's second term.

In the letter, they said McGurk ``lacks the leadership and management experience'' needed for the job.

The White House said it was standing by McGurk's nomination, which also was supported by the current ambassador to Iraq and his two predecessors.

``We believe that our nation will be greatly served by his experiences in Iraq and we look forward to the Senate's advice and consent on his appointment,'' White House press secretary Jay Carney told reporters.

In a letter to the Democratic chairman and the top Republican on the Foreign Relations panel, the current U.S. ambassador to Iraq, James Jeffrey, and former envoys Christopher Hill and Ryan Crocker defended McGurk and expressed their ``enthusiastic support'' for his nomination.

``We need an ambassador to Iraq,'' they said, according to a copy of the letter obtained by The Associated Press. ``Brett is the right man for the job. We hope that you will support him to the fullest extent possible, and we urge the Senate's swift confirmation.''

Earlier, Sen. John Kerry, the Democratic chairman of the committee, hinted that the nomination could be reconsidered. He said he had spoken with Vice President Joe Biden about McGurk. ``I think there are some very fair questions being asked and they need to be answered,'' Kerry said.

The six Republican senators said their ``strong concerns'' about McGurk's qualifications were amplified by emails detailing what they called his ``unprofessional conduct.''

The emails in question indicate that McGurk had an intimate relationship with a Baghdad-based female American journalist while he was married to another woman and working at the embassy there in 2008. McGurk has since married the reporter, Gina Chon, who resigned from The Wall Street Journal on Tuesday after acknowledging that she violated in-house rules by showing McGurk unpublished stories. McGurk has not responded to requests for comment.

``We believe the nominee lacks the leadership and management experience necessary to head America's largest embassy, in one of the world's most volatile regions,'' the senators' letter said.

McGurk was first assigned to the U.S. Embassy in Baghdad as a National Security Council staffer during the Bush administration and then led negotiations with Iraqi officials over an agreement that would govern security cooperation after U.S. troops left the country. The senators complained that McGurk had also alienated some Iraqi politicians.

``Finally, the public release of information detailing unprofessional conduct demonstrates poor judgment and will affect the nominee's credibility in the country where he has been nominated to serve,'' the senators said. ``Together, these issues cannot be overlooked. The U.S.-Iraq relationship is of the utmost importance to us, and we respectfully request that you withdraw this nominee and nominate someone with the qualifications necessary to ensure success in this position.''

The administration had defended McGurk, saying he is ``uniquely qualified'' for the post and that he had undergone a rigorous vetting process before being nominated.

The Senate Foreign Relations Committee is scheduled to vote on McGurk's nomination on Tuesday. From there it would be sent to the full Senate for a vote. But the fact that as many as six senators oppose McGurk suggests that at least one will place a hold on the nomination, which could kill it. Unless the hold was lifted, Obama would either have to withdraw the nomination or bypass Senate confirmation with a recess appointment.

The emails were not raised during McGurk's confirmation hearing last week.

Republican Sen. John McCain who is not on the foreign relations committee, criticized McGurk for his failure to negotiate a residual U.S. force in Iraq after combat troops left in December 2011. ``Iraq is unraveling as we speak,'' McCain said. ``He (McGurk) was part of that and so that's what my concern is.''

A former Supreme Court law clerk to the late Chief Justice William Rehnquist, McGurk worked as a lawyer for the Coalition Provisional Authority in Iraq after the 2003 U.S.-led invasion and joined Bush's National Security Council staff, where in 2007 and 2008, when the emails were written, he was the lead U.S. negotiator on security agreements with Iraq.

After a brief stint outside government with the Council on Foreign Relations, a think tank, he returned to Baghdad last year as a senior adviser to the current U.S. ambassador to Iraq, James Jeffrey.